The function of air assist fuel injectors is to provide enhanced atomization so that exhaust emissions can be minimized through more complete combustion. Prior designs, while providing better atomization, have failed to maintain accurate fuel spray targeting.
Fuel which wets the intake port impairs both emissions and driveability as the fuel film causes acceleration driving modes to be lean and decelerations to be rich. This problem is aggravated during cold engine conditions as the fuel film thickness is inversely related to port wall temperature. (The first two minutes of the cold engine phase of the emission test accounts for most of the emissions as the catalyst initially has zero conversion efficiency and tailpipe emissions are strongly dependent upon the raw emissions from the engine.)
While there are algorithms which compensate for this rich/lean condition, the finely atomized fuel which hits the port walls is not finely atomized when it flashes off the walls and/or runs down the walls. Thus much of the benefit is lost.
Known air assist fuel injectors for distributing fuel from a fuel injection valve in the vicinity of an intake port to two intake valves in a combustion chamber utilize a sleeve nozzle having fuel flow separating holes provided on the fuel injection downstream side of a fuel injection port means to separate a spray of fuel jetted from the fuel injection port means into flows in a plurality of different directions. The sleeve nozzle also has a plurality of slit-like air holes for jetting assist air in a band-like manner such that the assist air impinges against fuel sprays separately jetted from the fuel flow separating holes from the opposite sides of the fuel sprays. With this arrangement, flat jets of air impinge obliquely against the jetted fuel. With such an arrangement, the fuel cannot be directly targeted as a well defined spray.